The present invention relates to an apparatus for measuring the ground-contacting portion of tire tread and more specifically to a tire tread's ground-contacting portion measuring apparatus which measures with high precision the contact section of the tire tread pressed against a glass plate.
As an apparatus for observing or measuring the geometry of tire tread in contact with the ground, a device is known in which an illuminating device is arranged by the side of the glass plate edge and the tire is pressed against one of the surfaces of the glass plate to photograph the contacting geometry of the tire tread from the opposite surface of the glass plate by a camera.
With the above-mentioned tire-tread measuring apparatus, however, since the illuminating device is positioned close to the side edges of the glass plate, the heat from the illuminating device may deform the glass plate and, in the case of a laminated glass, may cause exfoliation at the joint. As a result, the picture image has non-uniform spots, making the high precision measurement of the tire-tread contact geometry difficult.
To solve this problem, it has been conceived to provide a cooling device to the illuminating device. Even this method can hardly maintain a stable measuring accuracy at all times and is disadvantageous in terms of cost.